Stabilized distillate hydrocarbon fuel oil compositions



United States Patent 3,268,311 STABILIZED DISTILLATE HYDROCARBON FUEL OIL COMPOSITIONS Roy L. Allen, Gresford, Wrexham, North Wales, and James H. T. Brook, Rockferry, Birkenhead, England, assignors to Shell Oil Company, New York, N.Y., a corporation of Delaware No Drawing. Filed Dec. 3, 1962, Ser. No. 241,516

Claims priority, application Great Britain, Jan. 25, 1962,

2,850/ 62 4 Claims. (Cl. 4472) This invention relates to liquid hydrocarbon fuels and in particular to distillate fuel oils, and is especially concerned with distillate fuel oils containing thermally or catalytically cracked products. By distillate fuel oil is meant a normally liquid mineral oil of which at least 98% volume can be distilled at a temperature not greater than 400 C. at atmospheric pressure, and having an ash of not more than 0.01% weight. It is an object of this invention to improve the stability of such fuel oils, i.e., to reduce their tendency to sludge deposition on storage for long periods.

According to the present invention a fuel oil composition comprises a distillate fuel consisting of up to 90% of a distillate fraction of a crude oil and 10% or more of a thermally or catalytically cracked product, and a small amount of one or more thiuram disulfides having on each nitrogen atom at least one substituent alkyl group of 5 or more carbon atoms.

These thiuram disulfides have been found to reduce substantially the tendency for sludge deposition of fuel oils and are greatly superior in this respect to other additives for the purpose, even closely related compounds such as alkyl substituted thiuram disulfides containing less than 5 carbon atoms per alkyl group, and alkyl and other substituted dithiocarbamates, as will be shown hereinafter.

To summarize, the thiuram disulfides which are useful in accordance with this invention are those having the formula R1 S H N C S: R2 2 wherein R is an alkyl radical having from 5 to 18 carbon atoms per molecule and R is selected from the group consisting of hydrogen or alkyl radicals having from 1 to 18 carbon atoms per molecule. The thiuram disulfides which are most effective, however, are those containing four alkyl substituents on the two nitrogen atoms of the molecule. In the foregoing generic structural formula, both R and R which are independently selected, are preferably alkyl radicals having from 5 to 18 carbon atoms per molecule. Tetra-N-alkyl-substituted thiuram disulfides in which the alkyl groups are the same are still further preferred. The thiuram disulfides with which the invention is concerned are readily made by oxidation of the corresponding dithiocarbamic acid with iodine.

The additive has been found to be effective in concentrations from 0.1 to 50 millimoles per liter of fuel. Surprisingly, a concentration range of from about 0.25 to millimoles per liter has been found to give generally more effective results, and a range of from about 0.5 to about 5 millimoles per liter is still more effective and is therefore preferred.

This inventioin is particularly applicable to blended distillate fuels containing thermally or catalytically cracked products, which blends are exceptionally prone to sludge or sediment deposition, and which may block the filters or orifices of equipment used to burn the fuel. It appears that minor constituents of the various components of the 'blend interact with each other to produce an amount of sludge much greater than would be expected from" the ice sludging tendencies of each component taken separately, one example of such a distillate fuel blend is a diesel engine fuel blend comprising 50% of a straight run distillate and 50% of a catalytically cracked product. However, it is to be understood that 100% catalytic cracked products are not to be excluded since, as will be shown hereinafter, reduction of sludge deposition in these products is also achieved by the additives of the present invention. All these products contain sulfur compounds, often in the form of mercaptans, and also various olefinic and aromatic compounds.

The following are examples of fuels in accordance with this invention which have been made and tested:

EXAMPLE I A light catalytically cracked cycle oil (LCCCO) having a mercaptan content of 538 parts per million measured as sulfur and 129 parts per million total nitrogen, which base fuel contains tetraamyl thiuram disulfide at a concentration of 10 millimoles per liter of fuel.

EXAMPLE II Equal parts of a LCCCO and a light straight run gas oil (LSRGO), having a mercaptan content of 376 parts per million measured as sulfur and 116 parts per million total nitrogen, which base fuel contains tetraamyl thiuram disulfide at a concentration of 10 millimoles per liter of fuel.

EXAMPLE III Equal parts of a LCCO and a medium straight run gas oil (MSRGO) having 124 parts per million basic nitrogen and 148 parts per million total nitrogen which base fuel contains tetraamyl thiuram disulfide at a concentration of:

(a) 1 millimole per liter of fuel.

(b) 10 millimoles per liter of fuel.

The improved quality of these fuels can be assessed by determining the amount of sludge developed in the fuel after it has been stored in cans under natural conditions for a known period. The fuel is filtered through a special paper having a controlled pore size of 0.45 micron, and the sludge is washed with light petroleum naphtha (60 C. b.p.). The paper and sludge is then dried at 103 C. for one hour, cooled and weighed. The weight of the paper filter, previously determined after drying for one hour at 103 C., is deducted to obtain the weight of the suspended sludge in the fuel. Sludge adhering to the can is dissolved in ethanol, the solvent is removed by evaporation, the sludge is dried at 103 C. and weighed. These quantities are then summed to give the amount of developed sludge in milligrams per milliliters of fuel. In addition to this sludge, a further quantiy can be precipitated by diluting the filtered fuel with 10 parts by volume of light petroleum naphtha (3040 C. b.p.). This is then allowed to stand overnight and is then determined in the same way as the suspended sludge. This additional sludge has a chemical composition similar to that of the suspended sludge, and may be either the precursor of the fully formed sludge, or a fully formed sludge which remains dissolved in the fuel only because of the aromaticity of the fuel; when the aromaticity is decreased by dilution the sludge precipitates.

In the following tables, which further illustrate the present invention, the sludging tendency of the fuel is taken as the sum of the three typs of sludge hereinbefore described.

Table I shows the results of tests carried out on BX- amples I and II, and on the base fuels used in'these examples containing substituted dithiocarbamates in place of tetraamyl thiuram disulfide, the results are expressed as a percentage of the control, i.e., fuel without additive.

3 The blends were stored by the filtration and ethanol procedure previously described.

Table I 4 EXAMPLE V A mixture of 60% by volume straight run gas oil containing 0.17% wt. sulfur and 72 ppm. nitrogen and 40% by volume oatalytioally cracked gas oil containing 1.36%

. wt. sulfur and 3 80 ppm. nitrogen and containing per i t (7 U Example Ibase fuel tendency parcent liter of gas oil mixture 1 millimole per liter of tetra- Without additive 100 hexadecanyl thiuram disulfide. With millimoles tetraam l thi uram disulfide/ liter y 22 EXAMPLE vi With l0millimoles p iperidinium pentamethylene 10 A mixture of tl:aight f f Cracked flistillaie ydithiocarbamate/liter 2 drocarbons containing 0.5 millimole per liter of tetra- With. 10 minimoles dibutyl ammonium dibutyl decanyl thiuram disulfide, the mixture having the fol- .dithiocarbamate/liter 46 lowing composition and component properties:

Example II base fuel: Hydng I treate Cat. Straight l qq 100 Light Cracked Run Gas With 10 millimoles tetraamyl thiuram disulfide/ fifi Gas 011 011 hter 14 Component Properties Distillate With 10 millimoles piperidinium pentamethylene dithiocarbamate/liter 46 Percent by Volume With 10 millirnoles dibutyl ammonium dibutyl dithiocanbamate/liter 43 15 5g 35 It is evident from the above table that the tetraallryl Gravity; 4M 2&8 32.9 thiuram disulfide of this invention is much more effective li igrcaptan s x l f ur, all )8 00- 0. 0005 8.8882 00 8 I- 10p lel'lO ll! g. CC than the substltuted dlthl ocarbamau?s- Disulfide Sulfur, f/ioo cc 0.0002 0. 0052 0. 010 Further tests were carried out to illustrate the superi- Total L p rc wt 0.1 5 0.92 0.90 f 1 Lfid f ASTM Distillation, F.: ority o tetraamy turam isu e, as an a i we or Inmal Bmhng pomt 386 444 456 reducing sludge deposition in fuel oils, over tetraalkyl Egg n ggggzgigg fig :32 2?? substituted thiuram disulfide containing shorter (i.e., less 1 Reqoveredjjjn 500 596 Q10 than 5 carbon atoms) alkyl chains. The results are End Pomt 534 640 (132 shown in Table II.

Table II (STORAGE TEMPERATURE 25 C.)

Storage Devel- Precip- Total Period oped tated Sludge Sludge Sludge 3 months Example I Base Fuel without additive 6. 2 8.5 14.7

Example I Base Fuel plus 10 millimoles/liter:

Tetramethyl tliiurain disullide 52. 0 14.2 66. 2 Tetraethyl thiuram disulfide 8. 2 1. 7 9. 9 Tetrabutyl thiuram disulfide 10. 9 4. 5 15. 4 Tctraainyl thiurain disulfide 1. 7 1.6 3. 3

3 months Example II Base Fuel without additive I. 4. 2 2. 5 6.7

Example II Base Fuel plus 10 inillimoles/liter:

Tetraethyl tliiuram disulfide 5. 7 D. 5 6. 2 Tetrabutyl tliiuram disulfide- 1. 9 5. 2 7. 1 Tetraamyl thiuram disulllde 0.3 0.6 0.9

6 months Example II Base Fuel without additive 7. 6 3. 7 11.3

Example II Base Fuel plus 10 millimoles/liter:

Tetraethyl thiurani disulfide 13. 7 1. 5 15. 2 Tetrabutyl thiuram disulfide 11.0 3. 3 14. 3 Tetraamyl thiuram disulfide 1. 6 1. 8 3. 4

Table III shows the results when the fuels of Example III were stored for different known periods at a In addition to the above, it will be recognized that the N-alkyl substituted thiuram disulfide compounds with temperature of 25 C., and then tested for sludge dewhich the invention is concerned can be used in fuel oil position by the described methods.

compositions containing hydrogen treated petroleum frac- T able III 3 Months 6 Months 9 Months 12 Months Storage Period Fuel of Fuel of Fuel of Fuel of Example Example Example Example Example Example Example Example Example Example Example Example without Illa. 1111) without IIIa IIIb without 111a 1111) without IIIa IIIb Additive Additive Additive Additive Developed S1udge 6. 1 0. 1 3. 2 6.9 0. 8 2. 5 7. 7 1. 2 6. 3 11. 6 1. 7 Precipitated Sludge... 3. 2 0.0 1. 4 4.0 1. 4 1. 2 4. 5 2. 0 2.8 6. 3 1. 3 Total Sludge 9. 3 0. 1 4. 6 10. 9 2. 2 3. 7 12. 2 3. 2 9. l 17. 9 3. 0

Other examples of fuels in accordance with the invention are as follows:

EXAMPLE IV A light catalytically cracked gas oil containing 0.99% wt. sulfur and 190 parts per million (p.p.m.) nitrogen and containing 5 millimoles per liter (basis gas oil) of N,N'- diethyl-N,N'-dioctyl thiuram disulfide.

tions, which may be either straight run or cracked fractions, and which have been treated with hydrogen for any number of purposes such as removal of metallic contaminants, reduction or removal of sulfur compounds, reduction of nitrogen compounds, or to adjust physical properties such as molecular weight, viscosity or pour point.

We claim as our invention:

1. A liquid hydrocarbon distillate fuel oil composition containing at least 10% by volume of normally liquid hydrocarbons produced from the cracking of petroleum hydrocarbons and from 0.1 to 10 millimoles per liter of said composition of a thiuram disulfide corresponding to the structural formula wherein R and R are independently selected alkyl radicals having from 5 -to 18 carbon atoms per molecule.

3. A liquid hydrocarbon distillate fuel oil composition containing 'at least 10% by volume of normally liquid hydrocarbons produced from the cracking of petroleum hydrocarbons and from about 0.5 to about 5 millimoles per liter of said composition of a thiuram disulfide corresponding to the structural formula wherein R and: R are independently selected alkyl radicals having from 5 to 18 carbon atoms per molecule.

4. A liquid hydrocarbon distillate fuel oil composition containing at least 10% by volume of normally liquid hydrocarbons produced from the cracking of petroleum hydrocarbons and from 0.1 to 10 millimoles per liter of said composition of tetraamyl thiuram disulfide.

References Cited by the Examiner UNITED STATES PATENTS 2,160,851 6/1939 Faust 4472 2,268,382 12/ 1941 Cloud 44-76 X 2,681,316 6/1954 Harle 252-47.5 2,691,632 10/1954 Harle 25247.5 X

DANIEL E. WYMAN, Primary Examiner.

C. O. THOMAS, J. E. DEMPSEY, Y. M. HARRIS,

Assistant Examiners. 

1. A LIQUID HYDROCARBON DISTILLATE FUEL OIL COMPOSITION CONTAINING AT LEAST 10% BY VOLUME OF NORMALLY LIQUID HYDROCARBONS PRODUCED FROM THE CRACKING OF PETROLEUM HYDROCARBONS AND FROM 0.1 TO 10 MILLIMOLES PER LITER OF SAID COMPOSITION OF A THIURAM DISULFIDE CORRESPONDING TO THE STRUCTURAL FORMULA 